This invention relates in general to electrophotography and, in particular, to an electrophotographic imaging member.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite imaging member comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor may also comprise additional layers such as an anti-curl back coating and an optional overcoating layer.
Multilayered belt photoreceptors tend to delaminate during extended cycling over small diameter support rollers. Alteration of materials in the various belt layers to reduce delamination is not easily effected because the new materials may adversely affect the overall electrical, mechanical and other properties of the belt such as residual voltage, background, dark decay, flexibility, and the like. Problems have been encountered in multilayered photoreceptors in which a substantially transparent photoreceptor is desired. One particular problem is that materials used to obtain a substantially transparent conductive layer, for example, cuprous iodide, do not adhere well to the materials used in the charge blocking layer. Thus, the layers tend to delaminate, resulting in failure of the device.
Another problem is the decrease in conductivity of certain materials used in the conductive layer. The present inventors have discovered that this problem may be associated with the materials used for forming the adjacent charge blocking layer A number of charge blocking materials are available for forming the charge blocking layer in a photoreceptor. One particularly effective type of material is siloxanes containing nitrogen. Various nitrogen-containing siloxanes are available as charge blocking materials, such as those disclosed in U.S. Pat. No. 4,725,518, No. 4,464,450, No. 4,599,286, No. 4,664,995, No. 4,639,402, and No. 4,654,284. However, the present inventors have discovered that the conductivity of materials such as cuprous iodide used in the conductive layer is diminished or destroyed by use of blocking layers containing nitrogen-containing siloxanes. A reduction in conductivity of the conductive layer is undesirable as it may result in a total failure of the device.
Accordingly, it is desirable to provide charge blocking materials for a photoreceptor which do not adversely affect the electrical and mechanical properties of the other layers of the device.